A similar thing happens on weekends - sometimes the bar is open, some other times it's purely a pay per drink type scenario up the back.
I doubt if you'd get the newspaper, but you'd get the normal meals etc.
TBH, I've never travelled CityFlyer on a public holiday, although once again, I've never seen any * on the Qantas site telling me that CityFlyer on Christmas is any different to CityFlyer the day [or 2 days] before.
The 25th December is a monday and so the bar should be free. When I have been on a flight on a bank holiday , I have found them try to charge; after speaking to the CSM and pointing out that Bank Holidays are not an exception to the Cityflyer drinks service according to the Cityflyer description, I have managed to get my drinks complimentary.
Seems like it is a paid bar on a bank hol unless you know that you should get freebies